1. Field of the Invention
The present invention relates to a module having a plurality of circuit boards stacked with a prescribed distance therebetween, in which an optical communication path is provided between the circuit boards. The present invention also relates to an optical connector providing an optical communication path that extends in a direction different from the axial direction of the optical communication path provided between the circuit boards.
2. Description of the Related Art
Modules are developed in which a plurality of circuit boards, onto which circuits made up of electronic and electrical components are built, are stacked with a prescribed distance therebetween. In this type of module, one circuit board and another circuit board are fixed via a fixing member to be mutually parallel. By stacking a plurality of circuit boards with intervening fixing members, it is possible to save space in the module compared to a case in which a plurality of circuit boards are disposed within one and the same plane. This type of module is used with the module enclosed in a housing or the like, for example when used in an on-vehicle information processing apparatus. There is a desire to transfer a large amount of information accurately between the stacked circuit boards. Japanese Utility Model Application Publication No. JP-U-5-77954 discloses a module having a light-emitting element provided on one circuit board and a light-receiving element provided on another circuit board that are disposed to be positioned in relative opposition in the stacking direction. In the art described in Japanese Utility Model Application Publication No. JP-U-5-77954, optical communication is implemented between circuit boards by the light-receiving element receiving an optical signal emitted by the light-emitting element. In the module described in Japanese Utility Model Application Publication No. JP-U-5-77954, an optical signal propagates in a space between the circuit boards.
In the module of Japanese Utility Model Application Publication No. JP-U-5-77954, it is difficult to achieve alignment in the stacking direction in the positional relationship between the light-emitting element and the light-receiving element. In this art, one circuit board and another circuit board are fixed by an intervening fixing member (called a supporting post in Japanese Utility Model Application Publication No. JP-U-5-77954). For this reason, if the fixing member and the light-emitting element are formed accurately with a pre-established positional relationship in the horizontal direction, and the fixing member and the light-receiving element are formed accurately with a pre-established positional relationship in the horizontal direction, it is possible to achieve positional alignment of the light-emitting element and the light-receiving element in the stacking direction. However, if either of the horizontal-directional position relationships is offset from the pre-established positional relationship in the horizontal direction, it is not possible to achieve alignment in the stacking direction. If circuit board expansion or contraction caused by a change in temperature or the like, the positional relationship between the light-emitting element and the light-receiving element changes, resulting in an offset from the positional relationship in which the light-emitting element and the light-receiving element are in mutual opposition. If the positional relationship between the light-emitting element and the light-receiving element is unstable, the transmission and reception of the optical signal is unstable. The stability of optical communication in the art of Japanese Utility Model Application Publication No. JP-U-5-77954 is poor. There is a need for the achievement of stable optical communication between stacked circuit boards.
In this type of module, it is necessary to provide an optical communication path between the outside and the optical communication path between circuit boards. This optical communication path is used when transmitting an optical signal from the outside towards the optical communication path between circuit boards and when transmitting an optical signal toward the outside from the optical communication path between circuit boards. In this type of module, it is often not possible to establish a sufficient space for installation. For this reason, the optical communication path provided between the outside and the optical communication path between circuit boards is often restricted with respect to installation space. It is therefore desirable that optical communication path provided between the outside and the optical communication path between circuit boards be able to cope with a restriction with regard to installation space.